Dynamic treatment with Leksell Gamma Knife Perfexion - A relaxed path sector duration optimization

Sammanfattning: Stereotactic radiosurgery is an increasingly popular method for treating brain tumours and lesions. The Leksell Gamma Knife Perfexion by Elekta is one of the leading instruments for stereotactic radiosurgery. Today the treatment with the Gamma Knife is performed in a static step-and-shoot manner, where several "shots" of gamma rays are delivered to specific regions within the tumour in order to cover it. The treatment generally requires many such shots and thus, in combination with the positioning between shots, the treatment becomes time consuming. There is an interest in a continuous dose delivery where the dose would be delivered through a continuous path through the tumour, i.e. a dynamic treatment. The notion is that this would shorten treatment times as well as increase plan quality and dose homogeneity within the tumour. A previous model for continuous dose delivery from 2014 poses the problem as path finding combined with an optimization of the speed along the path [1]. This thesis aims to improve that model by providing a new, smoothed path as well as allowing the path to be relaxed during the optimization. The findings show that treatment times can be significantly reduced and dose homogeneity as well as plan quality increased through dynamic treatment. The relaxation of the path during the optimization further improved all dynamic models. Furthermore, several interesting properties of dynamic treatment plans have been studied and presented including dose volume histograms, isodose curves and collimator settings.